1. Technical Field
This invention relates generally to displays for electronic devices, and more particularly to an electrophoretic display that has a front-side and back-side contrast ratio sufficient to be viewable by a user.
2. Background Art
The popularity of mobile telephones and other electronic devices, including computers, personal digital assistants (PDA), electronic games, and similar devices has increased the importance of components used to manufacture these products. As these devices have grown in popularity, consumers are demanding increased functionality in each device. For example, while mobile telephones once only made telephone calls, modern devices now take pictures, play music and video, and even games. At the same time, retail prices of these devices have continued to decrease, due in part to competition and market pressure. Manufacturers thus face a quandary: how to deliver devices with more functionality at a lower overall cost. To help resolve this problem, device manufacturers frequently demand reduction in the prices of components used to build the device. One component of particular interest is the display, due to its cost relative to the cost of the overall device. Device manufacturers are desirous of a low-cost, highly visible and easily configurable display technology.
A new type of display that has recently been developed is the electrophoretic display. Electrophoretic displays are manufactured by suspending particles in a medium, examples of which include gas, liquid, or gel, between two substrates. The particles may optionally be encapsulated in small capsules that are held between the walls, or they may be emulsified in a polymeric matrix. The particles have optical properties that are different from the medium in which they are suspended. Due to the electrochemical properties of the particles, and of the medium, the particles spontaneously acquire a net charge when placed in the medium. Having a charge, the particles will move in the presence of an externally applied electric field. Transparent electrodes, often in the shape of pixels, apply selective electric fields to the particles, thereby causing the particles to rotate and move to the viewable display surface. This movement causes an image to appear at the viewable display surface. Electrophoretic displays tend to be both very efficient in terms of electrical current consumption. Further they are generally available at a reasonable cost.
Certain mobile devices, including some mobile telephones, employ multiple displays to present information to a user. For example, a flip-style mobile telephone may include a first, small display on the outside of the device to present status information including phone signal strength, battery power indications, and caller identification information. A second, larger display is then provided inside the flip for viewing pictures, phone lists, text messages and the like.
One problem associated with conventional electrophoretic displays is that they are legibly visible only from one side. As such, devices employing multiple displays require multiple electrophoretic displays. This duplicity of components increases the overall cost of the device.
There is thus a need for a single, electrophoretic display capable of being used in devices having more than one display.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.